This invention relates to a remote control device for a trap circuit in a television community receiving system.
A TV and FM wave amplifier built in a casing is usually provided immediately below a TV and FM wave receiving antenna of a television community receiving system extensively employed today. The amplifier is provided with an FM trap circuit. In most of the amplifiers, the power necessary for operating the amplifier is supplied thereto through a signal transmitting coaxial cable from a power supply unit provided in the subscriber's house.
Such a conventional community receiving system is shown in FIG. 1, which comprises: a television (TV) wave and FM wave receiving antenna 1; an amplifier 2; a power supply unit 3; a television set 4; and a coaxial cable CX. In this community receiving system, the TV wave and the FM wave received by the antenna 1 are simultaneously amplified by the amplifier 2, and therefore the picture of the television set 4 is adversely affected by the cross modulation and intermodulation caused between the TV wave and the FM wave. In order to eliminate the difficulty, heretofore an FM trap circuit and a slide switch for connecting and disconnecting the trap circuit are provided in the amplifier, so that when it is not intended to receive an FM signal, the slide switch is operated to actuate the FM trap circuit to block the reception of the FM wave, so as not to adversely influence the television picture.
The essential components of the conventional amplifier and power supply unit are shown in FIG. 2, in which reference character t.sub.1 designates an input terminal for receiving a reception wave from an antenna (not shown), and reference character t.sub.2 designates an output terminal for the reception wave amplified, the output terminal serving also as a power supply input terminal. Between these terminals, a slide switch SW.sub.0 for connecting and disconnecting an FM trap circuit 6, an amplifier section 5 and a high-pass capacitor C.sub.6 are connected as shown in FIG. 2. The FM trap circuit is designated by reference numeral 6, and may be connected between the input terminal t.sub.1 and the amplifier 5 through the slide switch SW.sub.0. A choke coil L.sub.11, a diode D.sub.2 with the polarity as indicated and a DC power supply section 7 (including a voltage smoothing circuit and a constant voltage circuit) are connected between the amplifier 5 and a point P.sub.1 between the terminal t.sub.2 and the capacitor C.sub.6. The DC power supply section 7 feeds current to the amplifier 5. These elements surrounded by the one-dot chain l.sub.1 form a community receiving amplifier 2, and are built in a casing except for the slide switch SW.sub.0 which is provided on the outside of the casing. The amplifier 2 thus formed is provided immediately below the antenna on the roof. Components surrounded by the one-dot chain l.sub.2 in FIG. 2 form a power supply unit which is disposed in the subscriber's house or at a position in the vicinity of the house to which the subscriber can readily have access. The power supply unit has terminals t.sub.3 and t.sub.4. The terminal t.sub.3 is connected through a coaxial cable CX to the terminal t.sub.2 of the amplifier, and it serves as a terminal for receiving signals from the amplifier and also as a terminal for supplying current to the amplifier. The terminal t.sub.4 is to be connected to a television set (not shown). A highpass capacitor C.sub.7 is connected between the terminals t.sub.3 and t.sub.4. A choke coil L.sub.10 and the secondary coil L.sub.9 of a transformer T are connected in series between ground and a point P.sub.2 between the terminal t.sub.3 and the capacitor C.sub.7. The primary coil L.sub.8 of the transformer T is connected to the commercial power supply.
In operation, the 100 V commercial AC power supply voltage is dropped to 20-30 volts by means of the transformer, which is applied through the choke coil L.sub.10 and the coaxial cable CX to the amplifier 2, where it is applied through the choke coil L.sub.11 to the diode D.sub.2, as a result of which it is subjected to half-wave rectification and is then applied to the DC power supply section 7. In the DC power supply section 7, the voltage thus rectified is smoothed and is outputted as a constant voltage to operate the amplifier section 5. Then, an FM wave is selected by operating the slide switch SW.sub.0 provided outside the casing.
If in the case of observing a television picture, an FM wave is present, then cross modulation and intermodulation are caused between the FM wave and the TV wave as was described before, which will exert a bad influence on the television picture. Therefore, the slide switch SW.sub.0 is switched over to the trap circuit side to insert the FM trap circuit 6 in the signal circuit thereby to block the FM wave and to minimize the effect of the FM wave.
FIGS. 8(a) and 8(c) show the TV and FM wave transmission frequency bands in Japan and in USA, respectively. If the FM trap circuit is operated as described above, the FM wave is blocked as in FIG. 8(b) (in Japan) and in FIG. 8(d) (in USA).
As described above, the amplifier having the FM trap circuit and the slide switch for connecting and disconnecting the FM trap circuit is generally provided on the roof below the antenna. When the FM trap circuit is connected by operating the slide switch, the FM wave cannot be received. Accordingly, if it is required to receive the FM wave, someone has to climb on the roof to operate the slide switch to disconnect the FM trap circuit. This is hazardous and troublesome.